1. Field of the Invention
The present invention relates to electric load control systems employing occupancy or vacancy sensors for detecting an occupancy or a vacancy in a space, and more particularly, to a load control system including a radio frequency detector for detecting an occupancy or a vacancy in a space and a load control device for controlling the amount of power delivered to an electrical load in response to the detection of occupancy or vacancy.
2. Description of Background Art
Energy efficiency measures in buildings often utilize automated control systems that detect occupancy and/or vacancy conditions in a space and use such information to control electrical load devices, such as, for example, lighting fixtures, heating units, air conditioning units, ventilation units, or security systems.
Conventionally, load control systems employ occupancy sensors that detect motion within a space in order to determine the occupancy or vacancy condition. Some of the most common motion detection sensors include passive infrared (“PIR”) sensors, ultrasonic sensors and a combination of the two.
Such types of occupancy sensors, however, can only detect moving objects and usually require a direct line of sight between the sensor and the object. In the absence of occupant movements, the occupancy may remain undetected thus resulting in false triggering of the vacancy condition. Various objects within the space, room partitions or unusual room configurations can partially block the view of sensors and also cause false triggering. Improper sensor installation or changes in the room interior may also be a source of erroneous operation of the load control. When conventional occupancy sensors are used to switch lights on and off in a room, false triggering, inadequate sensor spacing, or view-blocking objects may cause a commonly observed condition when occupants are left in the dark.
The failures of occupancy sensors to detect vacancy condition often cause occupants' complaints, create work inefficiencies and may jeopardize occupant safety. All this slows the adoption of energy saving measures which rely on electric load control based on space occupancy.
It is therefore an object of this invention to provide an improved load control system which does not require the direct line of sight or object motion for occupancy or vacancy detection. It is another object of this invention to provide an independent method of detecting occupancy and/or vacancy in a space which can be used for improving the detection rate. The occupancy sensing load control system of this invention can be can be used in a stand-alone operation or can be integrated with other types of occupancy/vacancy sensing devices. Other objects and advantages of this invention will be apparent to those skilled in the art from the following disclosure.